Our laboratory has investigated the use of photodynamic therapy (PDT) for the treatment of thoracic malignancies by sensitization of malignant cells with a porphyrinoid (HPD) followed by illumination with 630 nM light. The in vitro sensitivity of human lung cancer line A 549 has been studied revealing that the cytotoxicity is dependent on the amount of energy input as well as the sentizer concentration used. A dose-rate effect has been revealed when cells were treated with .09 mW/cm2 vs. .27 mW/cm2. Cells incubated longer with the sensitizer had a significantly less surviving fraction by colony formation assay. Differences in in vitro sensitivity correlated with degree of cellular HPD concentration as measured by fluorescence, the protein concentration of the cells, as well as the size of the cells. Use of a light scattering media (intralipid) was able to augment the PDT cytotoxicity despite decreases in cellular HPD. Animal models of pulmonary metastases, tracheal tumors, as well as subcutaneous models have been established using the F344 rat sarcoma for the testing in vivo PDT. In vitro PDT of the F 344 rat sarcoma cell line has revealed it also to be sensitive to PDT. Two patients with complete bronchial obstruction due to metastatic malignancies have been palliated with PDT with partial or total lung expansion in both cases, without morbidity.